You can use a number of different methods to create a PO:
Direct creation of a PO: When the material is a regular item and market driven, order to a supplier can be created without an indent Directly from Indent option to create PO: In this option all items must be with the Purchase policy as ‘quotation not required’
Through Quotation Selection: A typical Purchase cycle with requirement, vendor selection and ordering
Trading Purchase Order: To fulfill a customer Sales order you can create a Purchase order. The PO is reserved to that Sales order
Releasing a rate contract: When a pre-agreed contract is available, you can release the contract to create the PO. You can also create a trading PO by releasing the order